A wind turbine known in the art typically comprises a wind turbine tower positioned on a foundation and with a wind turbine nacelle positioned on top of the tower. A wind turbine rotor, comprising three wind turbine blades, is connected to the nacelle through a low speed shaft, which extends out of the nacelle front as illustrated on FIG. 1.
The wind turbine tower typically comprises a number of round tower rings mounted on top of each other, where each tower ring is made of a steel plate rolled into a circular shape and welded to constitute a closed ring.
When the different sections, that constitute the wind turbine tower, have been transported to the site at which the tower is to be erected, the sections are connected by flanged joints. The flanges are provided with an array of through going holes which allow a large number of bolts and corresponding nuts to connect a tower section with the foundation or the next section.
A way to assemble sections of a wind turbine tower by using bolts and nuts is disclosed in international patent application No. WO-A 03/100268.
However, the height of wind turbine towers has increased significantly in the recent years and has increased the strength requirements of the flange joint connections. The number of bolts and corresponding nuts used in the flange joint connections has consequently also increased significantly.
The object of the present invention is to provide a technique which allows higher strength of the flange joint connections to be established with the same or less flange material to be used.